Initial Experience with the ViewRay System - Quality Assurance Testing of the Imaging Component

Purpose: The ViewRay system is a MRI-guided radiotherapy system. The first commercial ViewRay system (pending 510(k) clearance) is under installation at our institution. In this work, we present initial quality assurance testing of the 0.35T MR imaging component of the ViewRay system.

Methods: Quality assurance testing was performed on an ACR phantom following ACR recommendations. All testing was performed prior to installation of the 60Co sources. The phantom was placed at the isocenter of the MRI scanner. Sagittal localizer, axial T1 and T2 weighted scans were acquired. For all 3 scans, FOV was 250mmx250mm and the acquisition matrix was 256x256. TR and TE were 200ms and 20ms for the localizer, 500ms and 20ms for the T1 scan, and 2000ms and 20ms(80ms) for the T2 scan. The Localizer and T1 scan used spin echo acquisition and the T2 scan used double spin echo acquisition. 25 averages were used for T1 acquisition and 9 averages were used for T2 acquisition. The T1 scan was repeated with the prescan normalization option turned off to estimate the percent ghosting. Seven tests were performed including geometric accuracy, spatial resolution, slice thickness, slice position accuracy, image intensity uniformity, percent ghosting and low contrast detectability.

Conclusions: Although the ViewRay system is not designed for diagnostic purposes, our initial experience with its imaging component showed promising results. Quality assurance testing will be repeated following installation of the 60Co to confirm imaging performance.